Risk of damage when attempting to reduce CYA

Motozoic

Well-known member
Oct 30, 2018
45
Tucson, AZ
#1
I've been planning to perform a complete drain of my pool for several months in order to reduce my CYA levels, but the climate in Tucson has been excessively wet lately. Can anyone speak to the risk of floating a pool from high water table in this region? That would be totally disastrous, so I've been waiting for things to dry out for a few weeks before draining... except that it's been continuously wet with more rain and weather on the horizon.
 

mknauss

Mod Squad
May 3, 2014
12,273
Laughlin, NV
#2
I cannot speak for Tucson but here in the Colorado River valley there is no way to float a pool. The decomposed granite that composes our surface dirt is extremely porous.

Do you have large amounts of standing water? If you dig a hole to 3 or or 4 feet, will it fill with water?

An option to exchange your water versus draining and refilling is described below.

You can exchange some water without draining.

If you place a low volume sub pump in the deep end and pull water from there while adding water in the shallow end (through a skimmer or into a bucket on a step so you lessen the water disturbance) you can do a fairly efficient exchange. That is assuming the water you are filling with is the same temperature or warmer than your pool water. If your fill water is much cooler than your pool water, then switch it. Add the water to the deep end (hose on bottom) and pull water from the top step.

The location of the pump and fill hose may change if you have salt water, high calcium, etc.
In my pool, with saltwater and high calcium when I drain, I put the pump in the deep end and hose in shallow end. The water in the pool weighs more per unit volume than the fill water from the hose.

Be sure to balance the water out and water in so the pool level stays the same. Also be sure your pool pump is disabled during this process. Once started do not stop until you have exchanged the amount of water you wish.
 

ajw22

Gold Supporter
TFP Guide
Jul 21, 2013
3,269
Northern NJ
#3
Do you intend to drain and immediately refill or leave the pool empty for a while?

I think the risk of floating the pool is small if you immediately refill the pool. Or you can leave a foot or two of water which will get diluted on the refill. Getting a water truck load to quickly get water back in versus a slow fill from house hoses can also reduce risk.

I think if done smart and quickly the risk is small.
 

JoyfulNoise

TFP Expert
Platinum Supporter
May 23, 2015
14,513
Tucson, AZ
#4
Where in Tucson are you? There’s very little surface water here. Most wells are hundred of feet deep and the days of digging down 20ft and finding water are long, long gone. You can also lookup maps at the USGS website for detailed water depth analysis.

You don’t have to drain the pool. Simply drop a submersible pump in the deep end and a garden hose into your shallow-end skimmer with the pumps off (throw the breaker so they cannot run). The differential water temperature and TDS difference between the fill water and the pool water should be enough to keep both water layers fairly well separated. The inflow and outflow rates probably won’t match up (I’ll bet the submersible pump runs a little faster than the garden hose) so you’ll have to watch it and adjust as needed to keep the water level correct. But, if you can estimate the flow rates, then you can get a crude estimate of how much time you’ll need (a few days at most). I have a setup where I have flow meters on both and so I can accurately gauge my water exchange but it’s really overkill and not necessary unless you’re really interested in the numbers.

Once you exchange enough water, simply turn the pumps back on and let the water mix for a good 24 hours before testing again (brushing the walls will help homogenize the water). If you need to add salt for an SWG, then that will take a lot longer to mix up and homogenize in a cold pool. I wouldn’t bother doing that until the spring time when water warms up again. Even then, you often need 24-48 hours of continuos mixing to get the salinity levels fully homogenized.
 

slickraft

Well-known member
Oct 7, 2016
219
Phoenix
#5
I kept a 30,000 gallon plaster diving pool completely dry here in Mesa for almost 10 years and never had any issues except the plaster flaking (which was happening even before I drained it). I had it put back in service a few years ago with a new pebble-tech finish and there have been no issues. New homeowners said the pool is doing great. Lived here 30 years and never heard of anyone floating a drained pool around here.
 

Motozoic

Well-known member
Oct 30, 2018
45
Tucson, AZ
#6
We used to live near Starr Pass and that area was more mountainous and higher elevation, so drainage was great. We now live about 10 miles north of there near Ina & Wade Rd., it is significantly more moist and lower elevation here. Our backyard is a totally soggy mess, so I imagine that the soil surrounding the pool area is the same.

My plan was to use the pool filter pump in backwash mode and stick the vacuum head in the deep end to drain - I could either use the autofill valve to fill or I could restrict that and use a garden hose, not sure which one is faster or causes less disturbance. Does that sounds like a reasonable plan? According to pool math I need to replace 73% of the water to get the CYA down.

In the next few months I was also considering replacing my pool filter pump with a variable speed unit and replace the simple 2-way valve on the filter with a multiport. The waste feature of the multiport would be pretty handy right about now.
 

mknauss

Mod Squad
May 3, 2014
12,273
Laughlin, NV
#7
I would suggest following what I described above, and Matt reinforced, to exchange the water in your pool. I would not use the backwash setting on your filter for that extended of a time. It is not designed for that.
 

JoyfulNoise

TFP Expert
Platinum Supporter
May 23, 2015
14,513
Tucson, AZ
#8
You can purchase a 1/4 HP submersible pump for around $40 on Amazon or your local hardware store. 100ft of 1-1/2” poly discharge hose will help you get the water wherever you want it to go. Many sub pumps have garden hose adapters you can attach to them if you don’t want to buy discharge hose. If you don’t want to buy a sub pump, they can be rented from Home Depot (although, for the rental price, you may as well buy one). As Marty says, pool pumps are not intended for draining a pool and the flow rate differential will be way too high.

Up to you of course but I have owned a sub pump for years and find it to be a very useful tool to have around the house especially with a pool.
 

JoyfulNoise

TFP Expert
Platinum Supporter
May 23, 2015
14,513
Tucson, AZ
#10
I just bought this pump, 1 HP Stainless Steel Submersible Pump, Sump Pump - - Amazon.com, and made a 2" discharge fitting for a few bucks from Lowes. I haven't used the pump yet but it should be more than enough pump to drain my pool.
I got a 3/4 HP pump (plastic bodied with the float switch) and I glued together some 1” PVC pipe with unions to make an easy discharge line up and out if the deep end -

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It then hooks up to a 100’ of discharge hose but I get good flow (22 GPM) -

96099C3C-8843-46DA-BD9D-A3CD7E7F5EE4.jpg

I can choke the flow down to try match my 8 GPM garden hose but what I do is drain off about 600-700 gallons while refilling then shut the sub pump off and let the pool slowly refill through the skimmer. The skimmer weir door slows down the inflow of water and keeps the mixing to a minimum (as long as the pump is not running).

As I said, you can make it really complicated or simple but a sub pump is a useful pool tool.
 

Motozoic

Well-known member
Oct 30, 2018
45
Tucson, AZ
#11
That's fair enough. Issue is if I buy a submersible pump I'm going to want to get the best possible unit ever made LOL. I will look into it. I have a 50' 2" discharge hose already, but I might need something longer if the pump goes into the deep end.

On a related note, I tested draining the pool via the method I had initially described a few weeks ago. It worked, but I had to jumper the 2 ports in my skimmer to get it to work. This obviously required a very good seal on the tubing performing as a jumper between the main drain and the suction side. I'm really not sure how useful it is to have the main drain connected to the skimmer in that fashion - but it seems that this is common practice. Is it just a half assed attempt to hook up the main drain to "something is better than nothing?" The main drain is also attached to a valve that will drain into the sewer directly.
 

JoyfulNoise

TFP Expert
Platinum Supporter
May 23, 2015
14,513
Tucson, AZ
#12
It’s pretty common to see main drains tied to a skimmer as opposed to a direct line to the pad. It greatly reduces the chances of a suction entrapment since a body attempting to cover a drain would essential cause the pump to pull 100% from the skimmer thus relieving any suction pressure. However, from a hydraulic standpoint it basically renders the main drain useless as flow is greatly reduced. Given that split drains are standard code for pools nowadays, the main drain should really be plumbed directly to the pad but, as the saying goes, you can rarely teach old dogs new tricks.

A simple 1/2 HP sub pump, even a cheapo foreign made one, will be useful in many ways. If your home is prone to flooding, they come in very handy for moving water around. I got rid of my scuppers on the roof but, before I did, they use to create these large puddles around my house whenever it rained. The water would sit stagnant at my foundation for days after everything else was dried out and they became a source of mosquitos and termites. I would often run out and drain them using my sub pump just to keep the water away from my house. Now I use it for pool maintenance stuff and to drain a little fountain I have. I consider it to be a useful home tool to have around. I figure if I ever had a clogged bath tub, it would be fun to drain with the sub pump ...